Generally is impossible to stack infusions with one another. However, for the special case of the Enhanced Defense infusion, it has multiple possible targets, either a suit of armor or a shield. 

The infusion reads as follows. 

A creature gains a +1 bonus to Armor Class while wearing (armor) or wielding (shield) the infused item.

The bonus increases to +2 when you reach 10th level in this class.

Is it possible for a low-level artificer to infuse both a suit of armor and a shield and gain the bonuses to AC from both?

It does say OR very explicitly in the description so probably not.

Sadly you can't apply it to both your Armor and your Shield, because the general Infusion rules tell you that you can't:

You can infuse more than one nonmagical object at the end of a long rest; the maximum number of objects appears in the Infused Items column of the Artificer table. You must touch each of the objects, and each of your infusions can be in only one object at a time. Moreover, no object can bear more than one of your infusions at a time. If you try to exceed your maximum number of infusions, the oldest infusion immediately ends, and then the new infusion applies.

So even at 20th level when you can sustain a total of 6 Infusions, each of those Infusions must be unique -- you can't just use Enhanced Defense 6 times, only once.

now, what about two artificer working together, they can have both shield and armor, does it stack then?

Quote from dadame >>

now, what about two artificer working together, they can have both shield and armor, does it stack then?

 I'd probably allow it, but some dms might rule it's two identical sources (like two players casting bless) so only one boost applies.

Quote from dadame >>

now, what about two artificer working together, they can have both shield and armor, does it stack then?

I think that would be fine. The infusions specifically target the items - not the character wearing the items - and so they're not breaking the Combining Game Effects rule.

That said - I could absolutely see a DM disallowing it and wouldn't have any arguments.

thanks for the clarification!

I would still say no, it says while you're wearing/holding an item you get +1, not something like for each item you're holding/wearing.

Combining Game Effects

Different game features can affect a target at the same time.But when two or more game features have the same name, only the effects of one of them—the most potent one—apply while the durations of the effects overlap.For example, if a target is ignited by a fire elemental’s Fire Form trait, the ongoing fire damage doesn’t increase if the burning target is subjected to that trait again. Game features include spells, class features, feats, racial traits, monster abilities, and magic items. See the related rule in the “Combining Magical Effects” section of chapter 10 in the Player’s Handbook.

Enhanced Defense

Item: A suit of armor or a shield

A creature gains a +1 bonus to Armor Class while wearing (armor) or wielding (shield) the infused item.

The bonus increases to +2 when you reach 10th level in this class.

 
Despite the fact that the Infusion goes on the armor or shield, the effect gets applied to the creature who wears/wields the item. So if you ignore all of the irrelevant bits about which item got infused by whom and blahblahblah, it essentially comes down to one question:

Is this:

“Enhanced Defense. A creature gains a +1 bonus to Armor Class.”

the same thing as this:

“Enhanced Defense. A creature gains a +1 bonus to Armor Class.”

or not?

Yeah, I'm with Sposta: It's 2 of the exact same effect, so they don't stack.

Now, if the wording was changed to that it increased the AC granted by the item or some such, instead of giving a +1 AC to the creature using it, it may become stackable.

Edit: Forgot to mention, but the question on the poll seems really loaded to me.

Quote from UrthTheThoughtless >>

Yeah, I'm with Sposta: It's 2 of the exact same effect, so they don't stack.

Now, if the wording was changed to that it increased the AC granted by the item or some such, instead of giving a +1 AC to the creature using it, it may become stackable.

 Thank you. And agreed. If it said “The infused item provides an additional +1 bonus to your AC” or something similar then it would stack because one would be an “Enhanced Defense Shield” and the other “Enhanced Defense Armor.” Which is pro’ly exactly why they worded it the way they did.

Quote from UrthTheThoughtless >>

Edit: Forgot to mention, but the question on the poll seems really loaded to me.

 Also agreed.

the only way that you can get maximum AC bonus from your infusions woudl be Enhanced defence your armor and Repulsion Shield on your shield. this should be considered different sources and not conflict. this will give you a +2 or +3 to your ac depending on your level.

Enhanced defencd +1 AC (+2 at 10th) and Repulsion Shield +1 AC...

But if your over level 10 an don't have a +2 armor or shield.... must be a low magic world.

Quote from Tarzhay >>

 But if your over level 10 an don't have a +2 armor or shield.... must be a low magic world.

 
Unless the Artificer in the party only takes what they need from the loot and makes their own custom stuff for themselves instead of giving away their infusions like Oprah giving out cars. (Then they can predominantly use all their spells for buffing & support purposes instead of the other way ‘round.)